Arising of touch control technology has revolutionized portable electronic products. Referring to FIG. 1A, a conventional out-cell capacitive touch panel comprises a screen set 1 and a touch control set 2. The screen set 1 includes a first substrate 101, a transistor layer 102, a liquid crystal layer 103, a color filter layer 104, a second substrate 105 and a polarization layer 106 that are sequentially stacked. The touch control set 2 includes a third substrate 201, a touch control module 202 and a cover glass 4 that are sequentially stacked. Also referring to FIG. 1B, the touch control module 202 further includes a first electrode 202a, an isolation layer 202b, a second electrode 202c and a hard cover layer 202d that are sequentially stacked over the third substrate 201. The first electrode 202a and the second electrode 202c are made of transparent conductive material such as indium tin oxide (ITO) to respectively detect touch location in two different directions for confirmation. Because the touch control module 202 must be disposed onto the third substrate 201, the total thickness of the touch panel cannot be reduced. As nowadays the requirement for thin and light electronic products prevails, the difficulty in reducing the thickness of the touch panels has become the biggest issue in the industry. A great deal of effort has been devoted in the industry to reduce the thickness and production cost of the touch panel in order to meet use requirements.
To meet the aforesaid requirements, manufacturers have researched and developed One Glass Solution (OGS) technology of integrating the touch panel and display panel to reduce the total thickness. At present the in-cell touch panel has been developed that includes a touch sensor provided in the liquid crystal panel without adding an extra touch panel outside the liquid crystal panel, thereby reducing the total thickness significantly. However, the touch sensor occupies a portion of the display area, thus a part of the display effect is compromised. Moreover, fabrication process of in-cell touch panels is complex and production yield enhancement is difficult. Furthermore, U.S. publication No. 20120086665 entitled “Liquid crystal display device” discloses a technique of forming an electric field through a common electrode and a pixel electrode to detect user's touch and providing the touch control module disposed inside the liquid crystal panel to reduce total thickness. While this prior art does not have a reduced display area, disposing the touch control module inside the liquid crystal panel still complicates fabrication process and lowers production yield.
In order to solve the aforesaid problems, an on-cell touch panel that integrates the out-cell touch panel and the in-cell touch panel technologies has been proposed to overcome the problem of complex fabrication. Please refer to FIGS. 2A and 2B, the on-cell touch panel includes a first substrate 301, a transistor layer 302, a liquid crystal layer 303, a color filter layer 304, a second substrate 305, a touch control module 306, a polarization layer 307 and a cover glass 308 that are sequentially stacked. By directly disposing the touch control module 306 onto the second substrate 305 without the third substrate 201, the total thickness can be reduced. Moreover, the difficulty of disposing the touch control module 306 onto the second substrate 305 is far less than the fabrication process of the in-cell touch panel, hence this technique is widely accepted and extensively adopted in the industry. However, as the on-cell touch panel has to be fabricated layer by layer, it is time-consuming and results in slow production speed. Furthermore, in the event that the touch control module 306 disposed onto the second substrate 305 is tested to have poor touch detection effect at a test stage, the entire set of the touch panel has to be discarded. Therefore, the total production yield lowers and production cost increases. In addition, as the thinner substrates cannot withstand high temperature processes during fabrication, the electrode of the touch control module 306 is hard to be fabricated onto the second substrate 305, thereby increasing the difficulty of the production process.
Hence how to effectively reduce the total thickness, decrease the fabrication complexity and production cost, and increase the production yield and efficiency of the touch panel has become a common goal of the touch panel producers.